Polycrystalline diamond compacts (PDCs) have found particular utility as superabrasive cutting elements in rotary drill bits, such as roller-cone drill bits and fixed-cutter drill bits. A PDC cutting element typically includes a superabrasive diamond layer commonly known as a diamond table. The diamond table is formed and bonded to a substrate using a high-pressure/high-temperature (“HPHT”) process. The PDC cutting element may be brazed directly to a bit body, such as in a pocket formed on a blade or other feature of the bit body. The substrate of the PDC may be brazed or otherwise joined to an attachment member, such as a cylindrical backing. A rotary drill bit conventionally includes a number of PDC cutting elements affixed to the bit body. It is also known that a stud carrying the PDC may be used as a PDC cutting element when mounted to a bit body of a rotary drill bit by press-fitting, brazing, or otherwise securing the stud into a receptacle formed in the bit body.
PDCs are conventionally fabricated by placing a cemented carbide substrate into a container with a volume of diamond particles positioned on a surface of the cemented carbide substrate. The container may be loaded into an HPHT press with the substrate and volume of diamond particles then being processed under HPHT conditions in the presence of a catalyst material that causes the diamond particles to bond to one another to form a matrix of bonded diamond grains defining a polycrystalline diamond (“PCD”) table. The catalyst material is often a metal-solvent catalyst (e.g., cobalt, nickel, iron, or alloys thereof) that is used for promoting intergrowth of the diamond particles.
In one conventional approach, a constituent of the cemented carbide substrate, such as cobalt from a cobalt-cemented tungsten carbide substrate, liquefies and sweeps from a region adjacent to the volume of diamond particles into interstitial regions between the diamond particles during the HPHT process. The cobalt acts as a metal-solvent catalyst to promote intergrowth between the diamond particles, which results in formation of a matrix of bonded diamond grains having diamond-to-diamond bonding therebetween. Interstitial regions between the bonded diamond grains are consequently occupied by the metal-solvent catalyst.
The presence of the metal-solvent catalyst in the PCD table is believed to reduce the thermal stability of the PCD table at elevated temperatures experienced during drilling of a subterranean rock formation. For example, the difference in thermal expansion coefficient between the diamond grains and the metal-solvent catalyst is believed to lead to chipping or cracking of the PCD table during drilling or cutting operations, which consequently can degrade the mechanical properties of the PCD table or cause failure. Additionally, some of the diamond grains can undergo a chemical breakdown or back-conversion to graphite via interaction with the metal-solvent catalyst.
One conventional approach for improving the thermal stability of PDCs is to at least partially remove the metal-solvent catalyst from the PCD table of the PDC by acid leaching. Despite the availability of a number of different PDCs, manufacturers and users of PDCs continue to seek improved thermally stable PDCs.
Wear-resistant, polycrystalline diamond compacts (“PDCs”) are utilized in a variety of mechanical applications. For example, PDCs are used in drilling tools (e.g., cutting elements, gage trimmers, etc.), machining equipment, bearing apparatuses, wire-drawing machinery, and in other mechanical apparatuses.
For example, rotary drill bits employing polycrystalline diamond compact (“PDC”) cutters are often employed for drilling subterranean formations. Conventional drill bit bodies may be formed of steel or may comprise a so-called tungsten carbide matrix including tungsten carbide particles distributed within a binder material.
Tungsten carbide matrix drill bit bodies may be fabricated by preparing a mold that embodies the inverse of the desired generally radially extending blades, cutting element sockets or pockets, junk slots, internal watercourses and passages for delivery of drilling fluid to the bit face, ridges, lands, and other external topographic features of the drill bit. Particulate tungsten carbide may then be placed into the mold and a binder material, such as a metal including copper and tin, may be melted into the tungsten carbide particulate and solidified to form the drill bit body. Steel drill bit bodies may be fabricated by machining a piece of steel to form generally radially extending blades, cutting element sockets or pockets, junk slots, internal watercourses and passages for delivery of drilling fluid to the bit face, ridges, lands, and other external topographic features of the drill bit.
In both matrix-type and steel bodied drill bits, a threaded pin connection may be formed for securing the drill bit body to the drive shaft of a downhole motor or directly to drill collars at the distal end of a drill string rotated at the surface by a rotary table, top drive, drilling motor or turbine.